1. Field of the Invention
The present invention relates to a battery pack and more particularly to the battery pack that can be suitably used for a portable terminal device such as a portable cellular phone being carried by for example a user who is on the road over an extended period of time.
The present application claims priority of Japanese Patent Application No. 2002-079802 filed on Mar. 20, 2002, which is hereby incorporated by reference.
2. Description of the Related Art
Generally, a portable terminal device such as a portable cellular phone 1 is so configured as to operate using its dedicated secondary battery 20. For example, as shown in FIGS. 12A and 12B, the portable cellular phone 1 is made up of a main body of portable cellular phone 10 and the dedicated secondary battery 20. As shown in FIGS. 12A and 12B, the main body of portable cellular phone 10 has a battery mounting section 11, a multifunctional connector 12, terminals 13a and 13b, and an antenna 14. The dedicated secondary battery 20 is mounted in the battery mounting section 11. To the multifunctional connector 12 are connected a charging adapter used to charge the dedicated secondary battery 20, a personal computer, or a like. The terminals 13a and 13b are coupled to terminals 21a and 21b (not shown) of the dedicated secondary battery 20 used to take in electromotive force of the dedicated secondary battery 20. The antenna 14 is adapted to transmit and receive radio waves to and from a radio base station (not shown).
When the dedicated secondary battery 20 is discharged, if a user stays indoors and commercial power supply is available, the charging adapter is connected to the multifunctional connector 12 to charge the dedicated secondary battery 20. Moreover, when commercial power supply is not available in such a case where a user stays outdoors, conventionally, as shown in FIG. 13A, a battery pack 30 is connected to the multifunctional connector 12 to charge the dedicated secondary battery 20. The battery pack 30 serves as a simple charger or an emergency power source. The main body of portable cellular phone 10, as shown in FIG. 13B, includes a charge controlling circuit 40 and the internal circuit 50. The charge controlling circuit 40 feeds electromotive force of the battery pack 30 through terminals 13a and 13b and terminals 21a and 21b to the dedicated secondary battery 20 at a constant current and at a constant voltage for charging. Power of the dedicated secondary battery 20 is fed to an internal circuit 50 to perform main operations of a TDMA (Time Division Multiple Access)—type portable cellular phone.
FIGS. 14A, 14B, 14C, and 14D are circuit diagrams showing electrical configurations of the battery pack 30 in FIGS. 13A and 13B. Each symbol of batteries shown in FIGS. 14A, 14B, 14C, and 14D represents a cell unit of a battery and one cell has electromotive force of 1.5V.
The battery pack 30 shown in FIG. 14A is made up of three serially connected battery cells each having a voltage of 1.5 V for example, three pieces of alkaline accumulators) 31, 32, and 33. The battery pack 30 shown in FIG. 14B is made up of four battery cells 31, 32, 33, and 34 (for example, four pieces of alkaline accumulators, two pieces of serially-connected manganese dioxide lithium batteries each having a voltage of 3.0 V, or a like) each having a voltage of 1.5 V, a diode 35 for preventing backflow of a current, and a resistor 36 for limiting currents, being connected in series. The battery pack 30 shown in FIG. 14C is made up of six serially-connected battery cells 31, 32, 33, 34, 37, and 38 (for example, six pieces of alkaline accumulators, three manganese dioxide lithium batteries each having a voltage of 3V, one square-shaped stacked alkaline accumulator having a voltage of 9V, or a like) each having a voltage of 1.5 V, and a voltage dropping circuit 39 adapted to drop a voltage of the battery cells from 9V to 5V, all of which are connected in series. The battery pack 30 shown in FIG. 14D is made up of three battery cells each having a voltage that has come nearer to a final level and a voltage boosting circuit 3A adapted to boost the voltage of the battery cell up to a level of 5V, both being connected in series.
FIG. 15 is a circuit diagram showing electrical configurations of a charge controlling circuit 40 shown in FIGS. 13A and 13B. The charge controlling circuit 40 includes a current limiting circuit 41, a voltage limiting circuit 42, a limiting-type selecting switch 43, and a voltage detector 44. The current limiting circuit 41 limits a current flow of power to be fed from an AC adapter (adapter for charging) 60 adapted to convert a voltage (AC100V) of commercial power supply to DC 6V or from the battery pack 30 to a level that can be suitably used for charging the dedicated secondary battery 20 and outputs it. The voltage limiting circuit 42 limits a voltage of power to be fed from the AC adapter 60 or from the battery pack 30 to a level (for example, 4.5V) that can be suitably used for charging the dedicated secondary battery 20 and outputs it.
The limiting-type selecting switch 43 is used to select, based on a selecting signal SL output from the voltage detector 44, a power M of the current limiting circuit 41 and a power N of the voltage limiting circuit 42 and outputs the selected power. The voltage limiting circuit 42 outputs a voltage of a power Q output from the limiting-type selecting switch 43 and detects it and, based on a result from the selection, outputs the selecting signal SL. In this case, if a voltage of the power Q is higher than that being suitably used for charging the dedicated secondary battery 20, the power N of the voltage limiting circuit 42 is selected by the selecting signal SL, and if the voltage of the power Q is lower than that being suitably used for charging the dedicated secondary battery 20, the power M of the current limiting circuit 41 is selected by the selecting signal SL.
In the conventional portable cellular phone 1, when the battery pack 30 is connected to the multifunctional connector 12, the dedicated secondary battery 20 is charged at a constant current and at a constant voltage fed from the battery pack 30 through the charge controlling circuit 40, terminals 13a and 13b, and terminals 21a and 21b, and an electromotive force of the dedicated secondary battery 20 is supplied to the internal circuit 50. Operations of the TDMA-type portable cellular phone 1 are performed in the internal circuit 50. Moreover, when the AC adapter 60, instead of the battery cell 30, is connected to the multifunctional connector 12, the dedicated secondary battery 20 is charged at a constant current and at a constant voltage fed from the AC adapter 60 through the charge controlling circuit 40, terminals 13a and 13b, and terminals 21a and 21b. 
However, the above conventional battery pack 30 has following problems to be solved. That is, when a user goes the outdoors carrying the portable cellular phone 1 and the dedicated secondary battery 20 is already discharged and when commercial power is not available because the user is outdoors, the user has to perform charging the portable cellular phone 1 by using the battery pack 30, however, in this case, it will be time before a voltage of the portable cellular phone 1 reaches a specified level according to a state of the dedicated secondary battery 20 and therefore the portable cellular phone 1 does not operate immediately even after the connection of the battery pack 30. Another problem is that, since the dedicated secondary battery 20 makes up part of components of a power source section of the portable cellular phone 1, if a failure occurs in the dedicated secondary battery 20, the portable cellular phone 1 cannot be operated even by the connection of the battery pack 30.
Moreover, there is still another problem that, since the charge controlling circuit 40 is configured assuming that the dedicated secondary battery 20 is charged, if the dedicated secondary battery 20 is lost, the charge controlling circuit 40 does not operate normally in some cases and, as a result, a voltage required to normally operate the portable cellular phone 1 cannot be obtained even by the connection of the battery pack 30. Also, still another problem is that, since a voltage required for operating the charge controlling circuit 40 is 4V, it is necessary for the battery pack 30 to have at least three battery cells (each having a voltage of 1.5V) being connected in series, which thus causes a user to feel that the portable cellular phone 1 is heavy to carry. Furthermore, the conventional portable cellular phone presents another problem in that, when the battery pack 30 is connected to its multifunctional connector 12, other devices such as personal computers or a like cannot be connected to the multifunctional connector 12.
To solve these problems, a method is thought to be available in which another dedicated secondary battery having the same function as that of the dedicated secondary battery 20 and being in a fully-charged state is carried as a backup cell. However, this method has a problem in that not only carrying the dedicated secondary battery is attended with risk of occurrence of a short circuit but also buying such the backup dedicated secondary battery is costly. Moreover, in this case, a user has to carry an AC adapter required to charge such the dedicated backup second battery. Also, since the portable cellular phone 1 is operated according to the TDMA communication method, a judgement as to whether a voltage of the dedicated secondary battery 20 has reached its final voltage is made based on a voltage value that has dropped when power consumption increases or decreases in a burst manner. As a result, in some cases, a message that the voltage has reached its final level even in a state where a discharging depth of the dedicated secondary battery 20 is shallow (that is, battery capacity is still residual somewhat) appears on a displaying section of the portable cellular phone 1, which presents another problem that battery capacity cannot be used to the fullest.